A group of cross-hybridizing DNA segments contained within the EcoRI restriction fragments U', X and J of a Vero cell-adapted strain (BA71V) of African swine fever virus (ASFV) were mapped and sequenced. Analysis of the nucleotide sequence revealed the presence of a set of long internal repeated sequences composed of five types of tandemly repeat units of about 200 bp. These tandem repeats contain a G-rich core of 10-14 nucleotides surrounded by regions with a high A + T content distributed in oligo(dA).oligo(dT) tracts. Next to the repeated sequences we detected two related open reading frames that are members of a new multigene family (multigene family 300). Comparison of DNA sequences from several virus isolates indicated that this region undergoes frequent rearrangements leading to either duplications or deletions of the repeat units. These ASFV repeated sequences share similarities with chromosomal alpha satellite DNA, the scaffold-associated region and satellite III of Drosophila. Similar tandemly repeated sequences have not been described in other viruses.